Hi Nick,thanks for your note!I will check for another HDD. Strange enough that the current 3.5" HDD motor does not turn like the CD-drive motor. If the frequency is too high the motor stops turning and you hear a highfrequency noise ... Hopefully I found quickly a defect 4wire-HDD! Maybe the 2.5" HDD have different motors.Do you think an ESC could run my HDD? Can I use my powersupply ? Usually battery are used ... as far as I understood with PWM I can trigger the speed for the ESC. The ESC has usually 3 wires for the motor, that would fit to my HDD.Mirrors: I made the same experience in my tests, the CD as mirror maybe not good enough. In the end the glass mirrors are still the best (but maybe too heavy)!!I was also thinking how to calibrate the mirrors to the correct angles? you are right we need a special part. What angle are you using between the mirrors? With 5mm distance between the dot lines in 1m distance, we need 0.28 degree angle between the mirrors. Which is not much! (angle=5mm * 360 / (2 * 1000mm * pi).Thanks for joining the project - much more fun to make it together!

Do you think an ESC could run my HDD? Can I use my powersupply ? Usually battery are used ... as far as I understood with PWM I can trigger the speed for the ESC. The ESC has usually 3 wires for the motor, that would fit to my HDD.

Yes, I assume regular RC style ESC will run your HDD motor with no trouble. I am not sure about the supply voltages but it's safe to say that it would be more than 5V and less than 12V (unless you want to break the sound barrier with it ). If you have one, it may be a good match. In my case, I'm using the spin-up circuit as a kind of (uncontrollable) ESC - to say it differently, I want to keep the circuit that spins the disk and one that pulses the laser diode separate because I don't see how one Arduino MCU can handle both.

Mirrors: I made the same experience in my tests, the CD as mirror maybe not good enough. In the end the glass mirrors are still the best (but maybe too heavy)!!

Well, I would still stick to CD for safety reasons. I already had one mirror break off the holder at high RPM. You would NOT want this to be a high speed glass projectile - this just spells trouble. I don't know how stable the CD mirror will be in the long run - the surface had started to deteriorate where I was not careful enough to touch it - but it is so much safer than glass. It's up to you, obviously, but I will stick to your original plan!

I was also thinking how to calibrate the mirrors to the correct angles? you are right we need a special part. What angle are you using between the mirrors? With 5mm distance between the dot lines in 1m distance, we need 0.28 degree angle between the mirrors. Which is not much! (angle=5mm * 360 / (2 * 1000mm * pi).

Glad you brought it up! I am having problems with the 3D printed holder I got from Shapeways (arrived yesterday!) and that made me take a more careful look at the model. I originally had the faces at 1° to each other but you are correct, the lines would be too far apart. I was not sure how the 3D printed part would reproduce small angles but now that I got the part from Shapeways, I see that tiny angle differences will not be a problem at all. I have since re-done the model and created one with faces 0.25° apart. The only thing that remains to be seen now is how much the layer of glue under the pieces of CDs will affect the tiny angle variations.

If you like, you can order (I think - not yet an experienced enough Shapeways user) mirror holder here at my Shapeways page. This link leads to the 0.25° version. If you still need the 1° one, go to the link that shows all my Shapeways models (I only have two for now) and select the other one. If the ordering process does not work for some reason, please let me know, I want to make sure that people can get it there.

Sorry, paulosfjunior, I don't think I understood the question: are you asking if the scheme and the code, posted in the first message in this thread, are working? Yes, you can make the CD spindle motor work this way, although I have later moved onto using a different circuit because I switched to HDD motors and needed much faster rotation.

Please give me more details about your application (what are you building?) and I hope I may be able to help you better. If you like, you can start a new thread especially for your project.

I am looking to start an engine CD-ROM,'m following this schematic attached in the first mesagem the topic, I would like the code to start the engine without using the LED.

I'm using an Arduino Uno R3, 3 pairs of transistors (TIP31 and TIP32), 1k resistors and diodes (following the diagram you posted), but I can not understand the code, I just want the code to drive the motor.

The LED part of the code is completely independent of the part that turns the motors, it should just work even if you simply don't connect the LED without changing anything in the code.

The transistors you use should be strong enough to make the CD-ROM motor turn. Double check that they are connected properly. It's a pretty simple circuit, not much can go wrong as long as the parts are connected the right way.

If you change any part of this formula to make the resulting requestedStepDelay value smaller, the motor will rotate faster.

The reason I used a potentiometer is because some of BLDC motors have a hard time starting and working straight at the desired speed, most of the time they need to have the speed ramped up (relatively) slow so that the rotor does not skip commutation steps. This code is so simple, there's no provision for ramping up the speed. So, I manually increased RPMs with the potentiometer when I needed it. If you are looking to improve the code, implementing the gradual speed increase up to the desired speed is the first improvement it needs.

Reduce that value my small increments (decrements? ) because you can make it so fast that the rotor cannot catch up with the speed of commutation simply because of the inertia. Find the value that makes it start reliably, then bring it down little by little ( this is where you would really want that potentiometer!)

No, increasing voltage does not directly increase speed. Only if your motor is overloaded and is missing steps, then voltage increase may help. Otherwise the speed depends on how fast you change commutation of winding to go around full circle (the software does it 36 times per one revolution of the rotor)